This invention concerns a device for the crossed displacement of rolling rolls, whether they be working rolls and/or back-up rolls, as set forth in the main claim.
To be more exact, the invention is applied in cooperation with the upper and lower rolling blocks of a four-high rolling mill stand for plate and/or strip in order to permit a crossed and coordinated displacement of the working rolls and/or back-up rolls.
Rolling block in this case means the pair formed by the working roll and the back-up roll.
The state of the art covers four-high rolling mill stands for plate and/or strip which include opposed upper and lower working rolls which define the rolling plane and are fitted to the relative chocks located on one side and the other of the rolling mill stand.
Each working roll is associated with a relative back-up roll, the function of which is to limit the bends produced in the working roll during rolling, thus allowing very high rolling pressures to be used.
The state of the art covers the need to induce in the rolls a displacement in the rolling plane which causes a reciprocal crossed positioning of the rolls even though at very limited angles.
In the state of the art, this crossing movement is generally carried out by using two different techniques.
According to a first technique, traversing movements are imparted in a suitable direction to all the chocks supporting the rolls.
In order to achieve the crossed positioning of the rolls, each chock positioned at one end of a roll, for example a working roll, receives a traversing movement in the opposite direction to the movement imparted to the opposite chock of the same working roll and to the movement imparted to the chock at the same end of the opposed working roll.
By using this technique, the vertical projection of the point of intersection of the axes of the rolls remains unchanged for any angle imparted to the axes of the rolls.
According to another displacement technique, by displacing only the opposed chocks located on one side of the roll, while the chocks located on the opposite side are kept stationary, the position of the vertical projection of the point of crossover of the axes of the rolls is varied.
In the state of the art, a plurality of systems to displace the chocks have been proposed, for example with gear systems, screw-threaded systems, jack systems and others.
All these systems however have been found unsatisfactory with regard to accuracy of positioning, coordination of the movements, simplicity of embodiment and application, installation costs and other reasons, among which are the considerable power required, the considerable bending caused, the incorrect functioning of the bearings, etc.
Moreover, these systems known to the state of the art involve very long and laborious inspection and/or maintenance times, both because of their complex embodiments and also because of their positioning, as access is only possible with difficulty, or the maintenance/repair workers can only reach them after preliminary operations of at least partial dismantling of the rolling mill stand, carried out when the plant has been stopped, with all the technical and economic problems which that causes.
Another disadvantage is that devices known to the state of the art do not always manage to guarantee with maximum accuracy and in the long term the absolute equality of the crossing movements of the back-up roll and the relative working roll, for example due to different wear of the relative moving parts.
EP-A-0525552 describes a device which employs a plate, shaped like an inclined plane and vertically movable, which displaces intermediate blocks which are also shaped like an inclined plane at the sides, which in turn displace sideways the chocks of the back-up rolls or of the working roll/back-up roll combined.
This solution, although useful, requires a great force from the motor which moves the outer plates vertically, since it is necessary to transform the vertical movement of the outer plates into sideways movement on a horizontal plane of the intermediate blocks and therefore of the chocks.
Moreover, the sliding of the inclined plane surfaces involves a great deal of wear and therefore frequent maintenance is required or, if such maintenance is not performed, there is a deterioration in the accuracy of positioning.
EP-A-233597 describes a mechanism to laterally displace the working roll with respect to the relative back-up rolls or the intermediate rolls.
According to this system, the working rolls are not crossed over with respect to each other, they are displaced in the same direction so as to modify or regulate the offset and obtain a misalignment between the median vertical planes of the working rolls and the median vertical planes of the back-up or intermediate rolls.